There have heretofore been known many reports referring to processes for producing L-aspartic acid from fumaric acid and ammonia using aspartase as produced by microorganisms (Japanese Published Examined Patent Application Nos. 54-12553 and 57-18867). As such microorganisms, known are those belonging to the genera Escherichia and Corynebacterium, and some attempts have heretofore been made to obtain mutants with high aspartase productivity through genetic recombination technology (Japanese Published Unexamined Patent Application Nos. 60-133883 and 5-30977).
In the process for producing aspartase in a large amount using such microorganisms of the genera Escherichia and Corynebacterium, fumaric acid, which is expensive, is used as the nutrient source. In the process for producing aspartase using a transformant with high aspartase productivity as obtained through genetic recombination, antibiotics are added to the seed media for ensuring the stability of aspartase productivity of the transformant.
It is known that, when a microorganism of the type capable of producing and accumulating aspartame along with fumarase is used to produce aspartase and said aspartase is used for producing L-aspartic acid, some by-products other than L-aspartic acid are produced due to said fumarase to thereby lower the yield of the intended L-aspartic acid. In order to prevent the reduction in the yield of L-aspartic acid, the system is heat-treated or treated with acids after the production of aspartase to thereby remove fumarase activity from the system (Kagaku Kogyo, 58, 878, 1994; Japanese Published Examined Patent Publication No. 3-55103).
The prior art techniques are problematic in that processes, using microorganisms being capable of producing aspartase in order to produce-large amounts of aspartase, require fumaric acid, which is expensive, as the nutrient source; processes using transformants with high aspartase productivity as obtained through genetic recombination require antibiotics to be added to the seed media for ensuring the stability of aspartase productivity of the trasansformant; and in the processes for producing L-aspartic acid using microorganisms that may produce and accumulate fumarases in addition to the intended aspartase, the production of by-products other than the intended L-aspartic acid is inevitable.